Lithium ion polymer secondary battery its electrode and method for synthesizing polymer compound in binder used in adhesion layer thereof

Abstract

The present invention provides a lithium ion polymer battery comprising an electrode having excellent adhesion and electrical conductivity between a current collector and an active material layer, cycle capacity maintaining characteristics being improved, wherein a bonding layer, which bonds the current collector to the active material layer, is stable to an organic solvent in an electrolytic solution and is excellent in storage stability, and also, it is made possible to suppress the corrosion of the current collector by a strong acid such as hydrofluoric acid generated in the battery.

Description

TECHNICAL FIELD[0001]The present invention relates to a lithium ion polymer secondary battery which has a bonding layer between a current collector of an electrode and an active material, and a method for synthesizing a binder used in the bonding layer of the battery.BACKGROUND ART[0002]In recent years, thin batteries have been in increasing demand with the spread of portable devices, such as video cameras and laptop computers. A typical thin battery is a lithium ion polymer secondary battery which is formed by laminating a positive electrode and a negative electrode. The positive electrode is made by forming a positive electrode active material layer on the surface of a sheet-like positive electrode current collector, and the negative electrode is made by forming a negative electrode active material layer on the surface of a sheet-like negative electrode current collector. An electrolyte layer is interposed between the positive electrode active material layer and the negative elect...

AI Technical Summary

Benefits of technology

[0061]The secondary battery is excellent...

Problems solved by technology

Characteristics which the bonding layer is required to have include sufficient force of adhesion with the current collector material, sufficient force of bonding with the binder contained in the active material layer, stability in the presence of an organic solvent in the electrolytic solution, excellent long-term storage stability, thermal stability to remain without peeling when exposed to high temperature and electrochemical stability to endure repetitive charge-discharge cycles, but there has not been a solution that meets these requirements.

However, simply increasing the surface areas of the positive electrode sheet and the negative electrode sheet has a drawback of making the electrodes difficult to handle because of the large surface areas.

When the positive electrode sheet or the negative electrode sheet are folded or wound in a laminated state, the positive electrode sheet or the negative electrode sheet is bent along the folding line, thus causing the positive electrode sheet or the negative electrode sheet to peel off from the electrolyte layer, such as polymer electrolyte layer, which leads to a decrease in the effective surface area of the interface between the electrode and the electrolyte, resulting in decreasing charge capacity and internal resistance of the battery, thus deteriorating the cycle characteristics of the charge capacity.

Also, there has been a problem in that the current collector peels off the active material layer formed on the positive electrode sheet and the negative electrode sheet due to bending along the folding line.

Moreover, there has been a problem in that the positive and negative electrode active material layers expand and contract as the positive and negative electrode active material layers store and release lithium ions in the charge and discharge cycles, resulting in a stress that causes the active material layer to peel off the current collector.

However, the technique (1) has a problem in that butyl rubber, phenol resin or the like used as the binder is corroded with the electrolytic solution and peels off.

In the technique (2), although adhesive strength between the negative electrode current collector and the negative electrode material layer can be increased by forming the bonding layer containing, as a major component, acrylic copolymer containing a conductive substance mixed therein between the negative electrode current collector and the negative electrode material layer because an acrylic copolymer has high strength of bonding with PVdF contained in the negative electrode material layer and the negative electrode current collector, there has been a problem in that the acrylic copolymer is corroded by the electrolytic solution and the negative electrode current collector peels off the negative electrode material.

Although the technique (3) is claimed to increase the peel-off resistance and the number of 80% capacity cycles in the case in which polyurethane resin is used as the undercoat layer, the effect is not practically ...

Images